In recent years, much attention has been paid to a fuel cell system in which a fuel cell for generating a power by an electrochemical reaction of a fuel gas and an oxidant gas is used as an energy source. The fuel cell system supplies the fuel gas having a high pressure from a fuel tank to an anode of the fuel cell, and pressurizes and supplies air as the oxidant gas to a cathode thereof, to cause the electrochemical reaction of the fuel gas and the oxidant gas, thereby generating an electromotive force. The development of a vehicle in which such a fuel cell system is mounted has also proceeded. The fuel cell system to be mounted in the vehicle is constituted mainly of the fuel cell, a secondary battery, a running motor and auxiliary machines.
Meanwhile, in a usual electric vehicle, when a shift position is in a “drive (D)” range, a power is supplied from a battery to a running motor via an inverter or the like to rotate the motor, and the driving force of the motor is transmitted to a driving wheel. On the other hand, in a case where the shift position enters a “neutral (N)” range, the control by the inverter is stopped, and hence the running motor is left to idle, and brought into such a state as to generate a back electromotive voltage corresponding to a rotation number (referred to as the shutdown). That is, the running motor is rotated by the driving force conversely transmitted from the driving wheel, whereby the battery is charged with the generated back electromotive voltage via the inverter.
However, when the rotation number of the motor is large and the shift position enters the “N” range, an excessively large back electromotive voltage is generated, and an overvoltage is applied to the battery and a converter, which might deteriorate durability. To solve the problem in the conventional technology, control is executed so that when the shift position enters the “N” range and the rotation number of the motor is a predetermined threshold value or less, the shutdown is performed and so that when the rotation number is larger than the threshold value, the shutdown is not performed.
As a concerned technology, Patent Document 1 discloses a technology in which when the “N” position is selected, the excessively large back electromotive voltage is prevented from being generated. Moreover, to avoid a feel of difference due to the generation of a regenerative braking force, in the “N” position, target power calculation means uniformly sets a target voltage to zero, thereby preventing a driving torque or a regenerative torque from being generated by the motor.
[Patent Document 1] Japanese Patent Application Laid-Open No. 9-23508